John Campbell 
Invaders from the Infinite [EPUB ebook] 

The famous scientific trio of Arcot, Wade and Morey, challenged by the most ruthless aliens in all the universes, blast off on an intergalactic search for defenses against the invaders of Earth and all her allies. World after world is visited, secret after secret unleashed, and turned to mighty weapons of intense force, but it doesn’t seem enough. The invincible aliens savagely advance and the Earth team hurls bolt after bolt of pure ravening energy – until it appeared that the universe itself might end…